1. Technical Field
The disclosure herein relates to a redundancy circuit, and more particularly, to a redundancy circuit capable of repairing a defective cell.
2. Related Art
In general, when at least one defective memory cell exists in a semiconductor memory apparatus, the memory apparatus is regarded as a defective product that cannot be sold. Therefore, a redundancy technique for providing reserved memory cells in the semiconductor memory apparatus has been used. Conventional redundancy techniques include a method of providing laser fuse sets and using a laser beam to cut a fuse and thereby replace a bad memory cell with a replacement cell.
When a wafer manufacturing process is completed, a test process is performed to detect a defective memory cell, and a laser beam is irradiated to cut the fuse. Then, programming is performed. Positional information of the defective memory cell, that is, the address of the defective memory cell having the fuse cut, is stored, and the information is stored in a redundancy memory cell to replace the defective memory cell.
A defective memory cell may occur later in the packaging process. For example, a defective memory cell can occur due to an additional defect in the packaging process, or it can occur when the defective cell is not repaired by irradiation with a laser beam. However, the redundancy circuit controlled by the method of irradiating a laser beam cannot repair defective cells occurring in the packaging process.